This kind of cleaning devices are used for cleaning the interior of tanks and includes a drive system comprising a housing with a turbine mounted in a liquid channel to which cleaning liquid is supplied under pressure, as well as a gear which is driven by the turbine, and which is mounted separated from the cleaning liquid in the housing as a safeguard against leakage of cleaning liquid. The gear transfers the rotation produced by the turbine to a reduced rotation of a cleaning head in the tank. The rotation produced by the turbine is transferred to the gear via a magnetic coupling having coupling parts, the one coupling part of which being disposed inside the housing in the liquid channel and the other coupling part of which being disposed outside the housing, and wherein the coupling parts are mutually parallel discs.
The cleaning head includes a housing and a hub mounted thereon, and where the hub is provided with nozzles. The cleaning liquid being conveyed from the turbine and to the nozzles in operation, where the housing are mounted on a stationary mounting part so that the liquid from the turbine bypasses the housing and flows to the nozzles. The rotation of the turbine is transferred to the input shaft of the gear by means of a magnetic coupling having coupling parts, e.g. a hysteresis coupling, the driving coupling part of which being disposed outside the gear housing, and the driven coupling part of which being disposed inside the gear housing.
Jets of cleaning liquid are jets ejected by means of nozzles and pressurized liquid will clean the tank in an effective manner by their combined turning and rotation.
Examples of this kind of cleaning devices for tank cleaning are known from WO-A1-2007/076859, which describes a tank cleaning machine having a drive system comprising a hysteresis coupling having two magnetic parts formed by electromagnets, which magnetic parts are present inside the liquid space and outside this, respectively, a completely liquid-tight separation between the housing and the gear may be ensured. The magnetic part of the hysteresis coupling have a displaceable position of the one part relative to the other part the coupling may be adjusted with respect to the transferred torque and/or speed
One problem with the above tank cleaning devices having a hysteresis coupling is that when you adjust the speed on the hysteresis coupling by increasing or decreasing the space between the magnet parts and hysteresis plate or disc, the hysteresis torque will decrease when you increase the space between magnets and hysteresis plate.